Don't remember the size but it was the same wrench/screwdriver tool as a Gibson. Edit: Here it is. https://www.chicagomusicexchange.co...bOy01txeaeUp5xcjtwsPMZP3MgqC-MRxoCtHcQAvD_BwE
I had a "tube" wrench that came with mine but IIRC a thinwall 5/16" deep well socket also worked. I got one at Sears to fit my 1/4 square driver handle.
This works for some Foundations. Some 80s Foundations, not so much. The truss rod nut is sometimes too deeply recessed to be reached by a Gibson wrench.
On my 1984 Foundation, the Gobson wrench doesn’t work. I bought a cheap Stanley socket set at Walmart. The cheap thin wall socket was long enough and skinny enough to reach the nut. Getting the socket out of the truss rod channel can be...interesting.
On those types of wrenches, I've found I can gain some additional depth by taking a punch and hammer, and clearing out the little "petals" of metal in the socket area left by manufacturing... I bought a couple of these recently, and they worked just fine - but don't have the phillips screw driver end, though... 8mm 5/16 inch Truss Rod Box Wrench Spanner Repair Tool For Electric Guitar Gibso 191466916841 | eBay
I’m not sure how to say this without sounding indelicate. Consider that a parental advisory warning. I’ve never met another bass like my 1984 Foundation. I put the wrench in up to the shaft and still couldn’t reach the nut. The truss rod nut is somewhere between the string nut and the first fret, and it is closer to the first fret. I’ve never seen anything else like it.
